It has been found desirable in many instances to provide engines with a leaner than normal air/fuel mixture. Providing an engine with a lean air/fuel mixture is satisfactory in many running conditions, such as when the engine is idling, but does not provide sufficient fuel to support engine acceleration.
By way of example, a two-stroke engine creates exhaust gases, some of which mix in the scavenging process with the incoming air/fuel charge. These exhaust gases may contaminate the fresh incoming charge to an extent that complete combustion is prevented. The engine's power is reduced, and incomplete combustion of that charge further results in the engine's creation of exhaust which is highly polluted, aggravating the scavenging problem.
Also, during the scavenging process some of the fresh air/fuel charge is exhausted with the exhaust gases. The exhausting of unburned fuel in the air/fuel charge with the exhaust gases lowers the engine's power and contributes to air pollution.
In order to reduce these problems, the rate at which fuel is supplied to the engine is reduced. Combustion of this relatively lean fuel mixture produces a less polluted exhaust gas, reducing the contamination of the incoming air/fuel charge. Also, the lean air/fuel mixture which is exhausted contains less unburned fuel to pollute the atmosphere.
Providing fuel at a reduce rate is satisfactory when the engine does not require a great deal of fuel, such as when the engine is idling. However, when the engine speed accelerates, this solution is unsatisfactory since insufficient fuel is provided to the engine.
For example, planing-type watercraft require a greater amount of engine power to move them from their trolling (or resting) position to their planing position, than is required to maintain the watercraft's trolling or planing velocity. In certain types of boats, especially those known as personal watercraft, a problem arises in obtaining the necessary engine power to plane the boat using engines of the type described above.
A method and device for increasing the amount of fuel delivered to an engine during times of engine acceleration, while maintaining a low fuel delivery rate to the engine at other times, is desirable.